The field of the invention relates to current sensors for uninterruptible power supplies (UPS).
Typically, in a UPS with power factor correction, the current flowing into the frontend rectifier is made to be sinusoidal and inphase with the AC supply 12 voltage Vi. FIG. 1 illustrates, for example, a single-phase, boost converter-based UPS 10 which has front-end rectifier 15 wherein the current Ii flowing through the input inductor Li is measured by the current sensor 20. The switch S1 is controlled so that the current through the inductor Ii follows a sinusoidal shape and is in phase with the AC supply 12 voltage Vi. However, the configuration of the UPS circuit 10 fails to account for the non-linear current drawn by other circuits in the UPS system, such as a battery charger 18, which are connected between the AC supply 12 and current sensor 20.
U.S. Pat. No. 4,980,812 also describes a single phase UPS having a through-going neutral and power factor correction. The patented UPS achieves a unity power factor when the current through the line inductor is substantially similar to and in phase with the line voltage. However, the UPS described in U.S. Pat. No. 4,980,812 does not include any additional UPS components, such as a battery charger, connected to the source (mains) voltage. Thus, the UPS described by U.S. Pat. No. 4,980,812 also does not account for the non-linear currents of other circuits in a UPS system when attempting to improve the power factor.
Accordingly, a need exists for a UPS which is capable of operation at a unity power factor while accounting for and including elements on the UPS circuit in addition to a rectifier.